It is known, as for example from U.S. Pat. Nos. 725,853 of Borgmann and 2,016,353 of Wokosin, to form the top of a table of two separate normally coplanar panels having confronting inner edges that normally abut. A complicated guide mechanism is provided that allows these panels to slide apart, sometimes along with the respective legs, to form a gap which can be filled by a leaf. This leaf may itself be hinged in half and stored under the two main panels of the table. Such arrangements are normally relatively difficult to operate, requiring at least two people to separate the panels so the leaf can be put in place. The mechanism for sliding the panels on the table base is normally relatively complex and failure-prone, corroding with time so as to make sliding of these panels relatively difficult.
Another main type of expandable table has two panels similar to those described above, but each supported on four links that are all parallel and that each have one end pivoted on the table base adjacent a respective corner of the respective panel and another end pivoted on the respective corner. The panels can therefore be displaced through 180.degree. arcs from inner positions with their inner edges abutting to outer positions with their inner edges separated. Such a mechanism has proven extremely simple and efficient, making it relatively easy for one person to open up the table and add a leaf. The arrangement has the enormous disadvantage that any attempt to lift the table by means of the panels will tip them inward and dump anything on them toward the center of the table, all without lifting the base of the table off the floor until the panel has been raised quite a distance above the base.
Swiss patent No. 165,773 of Winkler discloses a table having a pair of panels supported by rigid pivot links so that these panels can be swung from a center position to an outer position. The panels move wholly pivotally, that is no part of them is constrained to straight-line movement. A leaf-spring arrangement holds them snugly in the outer position. The failing of this system is, once again, that the floppy panels are not adequately secured against upward movement so that, for example, an attempt to lift the table by the outer edges of the panels would merely tip these elements up.
U.S. Pat. Nos. 2,240,551 of Cooper, 1,927,282 of Hansen, and 1,849,092 of Hunter describe other standard slide-type arrangements with a raisable center leaf.